This project will investigate the feasibility of a passive-pumped Rankine cycle power generator suitable for use in a space nuclear power system. The system will operate on a thermodynamic cycle that is a modification of the conventional Rankine cycle, in which the normal boiler feed pump is replaced by a "passive pumping module" (PPM) and the working fluid is a suitable organic fluid. This new organic vapor cycle is attractive because it can be used effectively with medium temperature heat sources including radioisotopes, reactors, or solar collectors. The parasitic power required for the boiler feed pump in medium temperature conventional organic Rankine cycle power systems tested to date can be 20% to 30% of the system output power. By replacing the boiler feed pump by the PPM, the parasitic pumping power should be only 2% to 3% of the output power. 'Thus, the use of the PPM promises higher system efficiency, lighter weight, and higher reliability for small to medium size organic Rankine cycle power generators. A major part of the research will be to develop a zero-gravity PPM. A PPM has been developed that circulates freon in a terrestrial solar heating system. Also solar researchers at the Los Alamos National Laboratory have developed a similar PPM. The zero-gravity PPM will use features of the terrestrial PPMs already in use in advanced freon phase-change solar heating systems.Anticipated Results/Potential Commercial Applications as described by the awardee:This research is expected to develop an effective zero-gravity passive pumping module (PPM) that can replace the energy consuming boiler feed pump in organic Rankine cycle space power systems. The resulting passive-pumped organic Rankine cycle power system will be more efficient, more reliable, and should be lighter weight than a conventional system with a boiler feed pump and will be ideal for use in space with nuclear or solar heat sources. The results of the research will also allow more costeffective terrestrial Rankine cycle power systems for use with solar, nuclear, geothermal, or waste heat sources.
